In vivo two-photon fluorescence lifetime imaging microendoscopy based on fiber-bundle

Current optical imaging techniques often struggle to capture detailed physiological data from deep within living organisms. Researchers frequently encounter significant limitations when attempting to observe internal cellular environments without causing substantial tissue damage. Prior work has shown that standard microscopy methods lack the necessary portability for in vivo applications. No prior work had resolved the challenge of combining high-resolution fluorescence lifetime data with compact fiber-optic delivery systems. That uncertainty drove the development of specialized microendoscopic tools for biological research. Scientists have long sought ways to monitor the physicochemical properties of tissues in their natural state. This gap motivated the creation of systems that can penetrate deeper than traditional surface-level imaging devices. The current study addresses these technical hurdles by integrating advanced fiber-bundle technology into a functional, portable imaging platform.

The researchers aimed to develop a two-photon fluorescence lifetime imaging microendoscopy system for investigating biological microenvironments. They sought to overcome the limitations of traditional imaging by creating a compact, fiber-based device. The team focused on achieving cellular resolution while maintaining portability for in vivo use. This effort was motivated by the need to observe physiological processes within deep tissues naturally. The investigators addressed the challenge of delivering excitation light through a fiber-bundle without losing signal quality. They specifically designed the system to include an achromatic mini-objective for improved light collection. The study was driven by the goal of providing a tool that offers better contrast than standard intensity imaging. Ultimately, the authors intended to demonstrate the practical utility of their system for diverse biological applications.

The researchers constructed a specialized two-photon system by coupling a fiber-bundle to a standard microscope setup. They attached an achromatic mini-objective with a 1.4 mm diameter to the distal end of the fiber. A dispersion precompensation module was included in the laser source to optimize the excitation pulses. The team utilized 840 nm light to induce fluorescence within the biological samples. They performed Z-stack imaging on the intestine of a mouse injected with a specific squaraine dye. The investigators also targeted the kidney, liver, and xenografted tumors to test the system's depth capabilities. Data acquisition occurred at depths reaching 100 µm to ensure cellular resolution. This review approach confirms the technical feasibility of the proposed microendoscopic configuration for in vivo applications.

The system achieved a lateral resolution of 1.55 µm and a field of view measuring 390 µm. Researchers successfully captured Z-stack images of the intestine surface ranging from 0 to 130 µm in depth. The platform effectively visualized the kidney, liver, and xenografted tumors at a depth of 100 µm. Cellular resolution was maintained throughout these deep-tissue imaging sessions. The captured images displayed superior contrast compared to traditional intensity-based imaging techniques. This performance allowed for the clear mapping of cell distributions and complex tissue structures. The findings confirm the system's ability to measure fluorescence lifetime in situ within living organisms. These metrics highlight the successful integration of the fiber-bundle with the two-photon excitation source.

The authors propose that their fiber-bundle system effectively captures fluorescence lifetime data from deep within biological structures. This approach provides a clearer view of cellular distribution compared to traditional intensity-based imaging methods. The researchers suggest that their device serves as a robust instrument for investigating the microenvironment of living tissues. Their findings indicate that the system maintains high resolution even when imaging at significant depths in vivo. The team notes that the integration of dispersion precompensation enhances the quality of the captured fluorescence signals. These results imply that the technology is well-suited for studying various internal organs in a natural state. The study demonstrates that the platform can successfully visualize xenografted tumors with high contrast. The authors conclude that this microendoscopic design offers a versatile solution for future physiological investigations.